在谷歌云 Firestore 中获取 promise 中增加的计数器值

Question

I am trying to create a new invoice number by using the incremented counter value. How can I obtain the incremented value (in a promise) after incrementing it?

Below is the code that I am using to increment.

db.doc(docRef).update({numberOfInvoices: FieldValue.increment(1)});

Firestore counters

Answer 1

You need to query the document after you have updated it, as follows:

db.doc(docRef).update({numberOfInvoices: FieldValue.increment(1)})
.then(() => {
   return db.doc(docRef).get();
})
.then(doc => {
        console.log("Document data:", doc.data());
}).catch(error => {
    // ...
});

FieldValue.increment "returns a special value that can be used with set() or update() that tells the server to increment the field's current value by the given value". In other words, the calculation is done by the Firestore backend, and therefore you need to query the doc to get the new incremented value.

Answer 2

You can just get the incremented value by

let data =await db.doc(docRef).get(); //make sure the functions is async
let counts = data.val()['numberOfInvoices'];